Light History, Phosphorus Status, and the Occurrence of Light Stimulation or Inhibition of Phosphate Uptake in Lake Superior Phytoplankton and Bacteria

Publisher Website
Google Scholar
Abstract
Phosphate uptake in Lake Superior was stimulated by light on 17 out of 34 occasions, inhibited on 10, and unaffected on 7. In a stepwise multiple regression model the variables explaining most of the variance in the light effect on phosphate uptake were, in decreasing order of importance, the light history as estimated by hours of sunshine in previous 3 d, phosphate turnover time, phytoplankton biovolume, and time of day. Stimulation was most common in spring at inshore stations, while inhibition occurred mainly in spring at offshore stations. We suggest that light-limited but phosphorus-sufficient phytoplankton show the former, but extremely low light adapted populations, the latter response. We discovered an apparent diurnal pattern in the response, with maximal stimulation by light during daylight hours and inhibition predominating at sunrise and sunset.